
/*
 * Janino - An embedded Java[TM] compiler
 *
 * Copyright (c) 2001-2010 Arno Unkrig. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
 * following conditions are met:
 *
 *    1. Redistributions of source code must retain the above copyright notice, this list of conditions and the
 *       following disclaimer.
 *    2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
 *       following disclaimer in the documentation and/or other materials provided with the distribution.
 *    3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote
 *       products derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.codehaus.janino;

import java.io.FilterReader;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

import org.codehaus.commons.nullanalysis.Nullable;

/**
 * A {@link FilterReader} that unescapes the "Unicode Escapes" as described in JLS7 3.10.6.
 * <p>
 *   Notice that it is possible to formulate invalid escape sequences, e.g. "&#92;u123g" ("g" is not a valid hex
 *   character). This is handled by throwing a {@link java.lang.RuntimeException}-derived {@link
 *   UnicodeUnescapeException}.
 * </p>
 */
public
class UnicodeUnescapeReader extends FilterReader {

    public
    UnicodeUnescapeReader(Reader in) { super(in); }

    /**
     * Overrides {@link FilterReader#read()}.
     *
     * @throws UnicodeUnescapeException Invalid escape sequence encountered
     */
    @Override public int
    read() throws IOException {
        int c;

        // Read next character.
        if (this.unreadChar == -1) {
            c = this.in.read();
        } else {
            c               = this.unreadChar;
            this.unreadChar = -1;
        }

        // Check for backslash-u escape sequence, preceded with an even number
        // of backslashes.
        if (c != '\\' || this.oddPrecedingBackslashes) {
            this.oddPrecedingBackslashes = false;
            return c;
        }

        // Read one character ahead and check if it is a "u".
        c = this.in.read();
        if (c != 'u') {
            this.unreadChar              = c;
            this.oddPrecedingBackslashes = true;
            return '\\';
        }

        // Skip redundant "u"s.
        do {
            c = this.in.read();
            if (c == -1) throw new UnicodeUnescapeException("Incomplete escape sequence");
        } while (c == 'u');

        // Decode escape sequence.
        char[] ca = new char[4];
        ca[0] = (char) c;
        if (this.in.read(ca, 1, 3) != 3) throw new UnicodeUnescapeException("Incomplete escape sequence");
        try {
            return Integer.parseInt(new String(ca), 16);
        } catch (NumberFormatException ex) {
            throw new UnicodeUnescapeException("Invalid escape sequence \"\\u" + new String(ca) + "\"", ex);
        }
    }

    /**
     * Overrides {@link FilterReader#read(char[], int, int)}.
     */
    @Override public int
    read(@Nullable char[] cbuf, int off, int len) throws IOException {
        assert cbuf != null;
        if (len == 0) return 0;
        int res = 0;
        do {
            int c = this.read();
            if (c == -1) break;
            cbuf[off++] = (char) c;
        } while (++res < len);
        return res == 0 ? -1 : res;
    }

    /**
     * Simple unit testing.
     */
    public static void
    main(String[] args) throws IOException {
        Reader r = new UnicodeUnescapeReader(new StringReader(args[0]));
        for (;;) {
            int c = r.read();
            if (c == -1) break;
            System.out.print((char) c);
        }
        System.out.println();
    }

    private int     unreadChar = -1; // -1 == none
    private boolean oddPrecedingBackslashes;
}
